The present invention relates to a deflection control ink jet recording apparatus which ejects ink under pressure from a nozzle, applies vibration to the ejected ink to form ink droplets regularly, develops selectively a charging electric field according to an image signal when each ink droplet shapes itself, charges the ink droplets by the electric field, and deflects the charged ink ink droplet by a deflecting electric field. More particularly, the present invention is concerned with a device associated with a deflection control ink jet recording apparatus of the type having a linear arrangement of numerous ink ejection holes in order to determine proper levels of charging voltage.
Known ink jet recording apparatus of the type described may be classified generally into a two-value deflection control apparatus, a multi-value deflection control apparatus and a combined apparatus of the two mentioned. In the first or two-value apparatus, ink droplets for printing data are charged (or charged to a high level) while those which are not used for printing are left non-charged (or charged to a low level or to the opposite polarity) so that the recording droplets may be deflected to a large extent by a deflecting electric field to impinge on a recording sheet and the non-recording droplets may be captured by a gutter. Conversely, the non-recording ink may be deflected to a large extent to be captured by a gutter. In this type of apparatus, one nozzle is used for one picture element during the recording operation. In the second or multi-value apparatus, one nozzle is used for three or more picture elements (e.g. 5 mm and 40 dots, assuming 8 dots/mm) and recording droplets of ink are charged to three or more levels (e.g. 40 levels) to be deflected along three or more paths (e.g. 40 paths). In the third or combined apparatus, recording ink droplets are charged in the same way as in the multi-value process. However, this last-mentioned apparatus first deflects recording charged droplets using a deflecting electric field extending in the Y-axis direction so as to cause them to miss a gutter and then deflects them using another electric field in the X-axis direction in accordance with their charging levels, thereby printing out data in the X direction on a recording sheet with positional variations.
Meanwhile, ink to be ejected from a nozzle may be vibrated by any of three known systems: one which imparts pressure oscillation to the ink proper, one which imparts vibration in an intended direction of ink ejection to a nozzle plate having at least one ink ejection hole, and one which applies vibration bodily to an ink ejection head in an intended direction of ink ejection. The first system permits the use of a single nozzle plate having one ejection hole which is bonded to the leading end of a cylindrical electrostrictive vibrator, the other end of which is communicated with a pressurized ink supply box. It also permits the use of a nozzle plate having numerous ink ejection holes which is bonded to the front wall of a pressurized ink supply box in such a manner as to cover a slit provided to said wall of the ink supply box. One or more flat electrostrictive vibrators are mounted on one side wall of the box to impart vibrating pressure to ink inside the box. The second system employs a multi-apertured nozzle plate rigidly mounted to a pressurized ink supply box through an elastic member which is caused to vibrate by an electrostrictive vibrator. The third system drives a head bodily for oscillation by means of a motor, a solenoid device, an electrostrictive vibrator or the like.
A deflection control ink jet recording apparatus of any of the systems stated places a recording sheet at a relatively large spacing from its nozzle plate. For this reason, ink is pressurized to a level high enough for a droplet of ink from the nozzle to reach the recording sheet stably along a predetermined path despite its passage through the charging and deflecting electrodes. In order that ink droplets of a given diameter may appear regularly and follow their predetermined paths accurately, there must be stabilized and exactly controlled a variety of factors including the viscosity and pressure of ink, vibrating pressure, amount of charge and intensity of deflecting electric field. It is impossible, however, to hold all of such quantities under fully ideal conditions. This particularly results misalignment of actual deflection paths from reference deflection paths in the case of the multi-value deflection control which charges ink ejected from a single ejection hole to several different levels and drives them to different positions on a recording sheet.
Generally, an amount of deflection x.sub.di of ink droplets can be expressed as: ##EQU1## where K denotes a constant which depends on the deflecting electrodes, Q.sub.i an amount of charge of the ink droplets, m.sub.j a mass of the ink droplets, v.sub.dp a deflecting voltage, S.sub.dp a spacing between opposite deflecting electrodes and v.sub.j an ejection velocity of the ink droplets.
An amount of charge Q.sub.i can be expressed as: EQU Q.sub.i =k.multidot.V.sub.ci Eq. ( 2)
where k indicates a value dependent on the shape of the electrode, shape of the ink column, dielectric constant etc. It will be seen from the Eqs. (1) and (2) that the amount of deflection X.sub.di and then charging voltage V.sub.ci are proportional to each other and expressed by X.sub.di .varies.V.sub.ci. Stated another way, they hold a linear relation therebetween which can be represented by a straight line which passes through the origin of a graph.
The specific relation mentioned between the amount of deflection and the charging voltage forms the foundation of the present invention.